packet-generator new {
  name x
  limit 1
  node ip4-input
  size 64-64
  data {
    ICMP: 1.2.3.4 -> 5.6.7.8
    ICMP echo_request
    incrementing 100
  }
}

tr add pg-input 100
set interface ip source-check pg/stream-0
ip route 1.2.3.4/32 via pg/stream-0 0x01020304
ip route 5.6.7.8/32 via drop